Impacts of the Bottom Copper Layer of Direct-Bond Copper Substrates on the Partial Discharge Performance in Power Modules

This article studies the impacts of the bottom copper layer of direct-bond copper (DBC) substrates on the partial discharge (PD) performance of the power modules. Finite element simulation models of DBC samples with various layouts are developed, and their electric field distributions are compared and analyzed. The results show that by floating the bottom copper layer, applying half of the high voltage, or partially or completely removing the bottom copper layer, the maximum electric field concentrated at the triple point of DBC substrates can be significantly reduced. Multiple DBC samples are manufactured, and their PD performance is experimentally tested. The partial discharge inception voltage (PDIV) can be increased by more than 79% by completely removing the bottom copper layer. Experimental results show good agreement with the simulation analysis and verify the findings. A mimic power module employing the concept of completely removing the bottom-layer copper is made and tested for PD performance under IEC 60270 standard. Compared to the conventional power module structure, the PDIV of the new power module structure can be increased by 63%. The findings in this article can provide guidance and potential strategies to reduce the electric field in encapsulated DBC substrates, which will contribute to optimizing the insulation design of future medium voltage power modules.